Antibodies were prepared which are specific for nucleoside and polynucleotide sequences. These antibodies bind to single-stranded areas in nucleic acids and are highly specific for the nucleosides or nucleotide sequences to which they have been elicited. They will be used to study systems in which nucleic acids are a part or in which they function. Included are investigations on the architecture of metaphase chromosomes, and of transplation systems (both cell free and in cells). The antibodies will also be used to investigate base methylation processes in cells, to locate purine and pyrimidine bases and sequences in DNA by electron microscopy and to separate and isolate individual chromosomes.